Numerous designs for rotary fluid stream apparatuses have been developed and used. Variations in features from one design to another relate to the vessel to be cleaned or provide an improvement over prior art. Certain of the cleaning apparatus designs are disclosed in U.S. Pat. No. 3,637,138 to Rucker, U.S. Pat. No. 5,012,976 to Loberg, U.S. Pat. No. 5,092,523 to Rucker et al., U.S. Pat. No. 5,169,069 to Rucker et al., U.S. Pat. No. 5,954,271 to Le, U.S. Pat. No. 6,123,271 to Delaney et al., U.S. Pat. No. 6,561,199 to Gleeson et al. and U.S. Pat. No. 7,523,512 to Delaney et al.
The common operational theme in the cleaning apparatus disclosed in these patents and other cleaning apparatus known in the trade is that a pressurized fluid drives a gear train to cause a set of nozzles to rotate, and the fluid flows through a housing to be discharged from the rotating nozzles. The nozzles typically are driven by a gear train to rotate around two orthogonal axes simultaneously. As depicted in the above noted patents, rotary nozzle cleaning devices can be designed either with the gear train between the fluid inlet cap and the nozzle housing or with the nozzle housing between the fluid inlet cap and the gear train. The fluid must therefore be conveyed from a path in the core of the mechanism to the periphery of the mechanism in order to be discharged through the rotating nozzles. This core to periphery conveyance is enabled by a tubular component known as a stem. A circumferential series of perforations are formed through the stem wall. Details of a particular stem are disclosed in U.S. Pat. No. 5,012,976, incorporated herein by reference (the '976 patent). The stem configuration in the '976 patent is characterized as having “Z” shaped openings through the tubular wall with “Z” shaped separating bars between adjacent pairs of openings. The '976 patent teaches providing an equal amount of opening exposed to the nozzle housing throughout a 360° rotation cycle, therefore enabling a uniform fluid flow to the nozzles. While uniform fluid flow is clearly beneficial, it has been determined that the “Z” shaped separating bars are structurally inadequate. The “Z” shaped bars have been found to be prone to distortion or fracture if the stem is subjected to excess torque when being installed or if the stem is dropped on a hard surface. In a later development, a stem having multiple rows of small round openings has been used, as disclosed in U.S. Pat. No. 6,123,271. While this design reasonably overcomes the structural strength problem, the flow rate is sacrificed. Therefore, a need exists for a structurally solid stem for a rotary nozzle cleaning apparatus that allows a uniform and optimum fluid flow therethrough.